The production of organotin halides by reacting elemental tin with an organic halide in the presence of an 'onium compound catalyst has been described in a number of earlier specifications, for example British patent specifications Nos. 1,115,646, 1,053,996 and 1,222,642. These processes, which lead to an organotin product containing principally diorganotin halides, use the 'onium compound in only catalytic amounts. It is possible that the 'onium compound, for example tetrabutylammonium bromide, forms a halostannite salt with the tin, for example tetrabutylammonium halostannite, and that it is this halostannite salt which serves as the actual catalyst. According to these earlier specifications, such complex formed from the 'onium salt can be recovered and recycled after the organotin products have been separated.
The direct reaction of elemental tin, with an organic halide and comparatively large (reagent) amounts of an 'onium compound leads to an organotin product which consists predominantly of triorganotin halides, as described in our copending application Ser. No. 456,316, filed of even date herewith and entitled "Production of Organotin Halides", the disclosure of which is incorporated herein by reference. For making triorganotin halides, a reagent other than an 'onium compound may be used, for example a complex of an alkali metal ion or alkaline earth metal ion with a polyoxygen compound such as diglyme. The reagent, whether 'onium compound or diglyme complex or some other source of active halide ions that can form a nucleophile with tin species, (i.e., act as a nucleophile generator) can be generally characterized as having the formula EQU Cat.sup.+ X.sup.-
where Cat.sup.+ is a positively charged species and X.sup.- is a halogen anion selected from chlorine, bromine and iodine.
The stoichiometry of forming triorganotin halides using reagent amounts of Cat.sup.+ X.sup.- may be represented, for the case where tetrabutylammonium bromide is Cat.sup.+ X.sup.- and butyl bromide is the organic halide thus (wherein Bu represents butyl): EQU 2 Sn+3 BuBr+Bu.sub.4 NBr.fwdarw.Bu.sub.3 SnBr+Bu.sub.4 NSnBr.sub.3.
When reagent amounts of 'onium compound or alternative reagent are used, substantial quantities of a complex containing the tin, combined with or complexed with the Cat.sup.+ X.sup.- , are formed; but whether this complex is exactly the halostannite salt indicated by the above equation is not certain. Whatever the complex is, it is formed in large quantities.
In order to re-use the tin (and possibly other metals) and reagent contained in such complex, it is again desirable to treat the same for recovery of the tin and reagent as such.
The complex formed as a by-product in the direct reaction of tin with an organic halide in the presence of an 'onium compound or other compound of formula Cat.sup.+ X.sup.- is itself water insoluble. It is also insoluble in hydrocarbons, and this feature makes it possible to separate it from the hydrocarbon-soluble organotin halides by solvent extraction.
The single phase electrolyses of complexes of a similar nature, but involving indium, beryllium, zinc and tin are described in German patent No. 1,236,208. This reference describes a process for producing very pure metals on the cathode therein from less pure metals as anode. However, the resistivity of the electrolyte is discouragingly high (about 50 ohm-cm), and, therefore, the electrolysis must be operated at low and economically unattractive current densities (e.g., 6 mA/cm.sup.2).
A type of two-phase electrolysis system is described in U.K. No. 1,092,254. This system involves the electrolysis of an aqueous electrolyte in contact with a material of low electrical conductivity (typically 10.sup.-20 to 10.sup.-4 reciprocal ohms per centimeter) and substantial insolubility. One electrode is in contact with only the aqueous solution, whereas the other electrode is partially immersed in both phases. It is claimed that sufficient non-aqueous phase wets the latter electrode to be involved in the electrolysis, but the examples indicate that, again, only discouragingly low current densities can be achieved (27-75 mA/cm.sup.2).